Impact-modified blends of polycarbonate and aromatic polyesters are known.
U.S. Pat. No. 4,888,388, for example, describes compositions of polycarbonate, polyethylene terephthalate and a graft polymer based on a silicone-butyl acrylate composite rubber, which compositions are distinguished by improved low-temperature strength. Flame-resistant molding compositions are not described.
Impact-modified blends of polycarbonate and aromatic polyesters which have been rendered flame-resistant are also known.
JP 04 345 657-A2 describes mixtures of halogenated aromatic polycarbonate, aromatic polyesters and graft polymers based on silicone-acrylate composite rubbers. The molding compositions described in JP 06 239 965-A are also based on flameproofing additives containing halogen. In addition to aromatic polycarbonate and aromatic polyesters, they contain graft polymers based on silicone-acrylate composite rubbers, and halogenated epoxy resins. The molding compositions described in WO 94/11429 contain polycarbonate, polyester and a halogenated aryl phosphate as flameproofing additive. Also described are compositions that additionally contain methacrylate/butadiene/styrene elastomers having a core-shell structure.
Because molding compositions rendered flame-resistant with halogen-containing additives can cause corrosion of the tool during processing owing to the liberation of halogen-containing gases, and because they liberate corrosive hydrogen halides which are damaging to health during combustion, it is desirable to develop molding compositions that are rendered flame-resistant without halogens.
Impact-modified blends of polycarbonate and aromatic polyesters which have been rendered flame-resistant without halogens are also known.
JP 2001 031 860-A describes compositions which have high impact strength, resistance to chemicals and hydrolytic stability and which contain polycarbonate, a mixture of polyethylene terephthalate and polybutylene terephthalate, a graft elastomer having a core-shell structure, a silicate salt and, as flameproofing additive, stabilised red phosphorus and polytetrafluoroethylene (PTFE). Such molding compositions have inadequate strength for many applications and cannot be adjusted to light colours as are required by the IT industry, for example for casings for monitors, printers, etc.
U.S. Pat. No. 5,030,675 describes molding compositions of polycarbonate, polyalkylene terephthalate, emulsion-ABS graft polymers, phosphorous compounds as flameproofing additive and fluorinated polyolefins as antidripping agent. The molding compositions are distinguished by improved weld line strength but have a comparatively low level of impact strength. Furthermore, the flameproofing additives that are used have a tendency to bleed, which can lead to considerable disruptions to the processing operations.
The problem of the volatility of the flameproofing additive is solved by the use of oligomeric phosphoric acid esters, as is described in EP-A 0 594 021. The PC/ABS compositions described therein contain polyalkylene terephthalate as well as oligophosphoric acid esters and fluorinated polyolefin as flameproofing additive and exhibit good notched impact strength and stress cracking resistance, as well as high dimensional stability under heat and a fault-free surface quality. However, they generally exhibit inadequate weld line strength and a disadvantageous processing window, i.e. there is a marked impairment of important properties, for example resistance to chemicals, at higher processing temperatures.
The compositions described in EP-A 0 829 517, EP-A 0 884 366 and JP 08 073 692-A are also rendered flame-resistant with oligophosphoric acid esters. In addition to the flameproofing agent and optional further additives, the PC/PET molding compositions described therein contain a graft polymer having methyl methacrylate in the graft shell. MBS and MMA-grafted polybutadiene rubber are described as examples of such graft polymers. The molding compositions described in those documents are distinguished inter alia by improved resistance to chemicals and oils.
The object of the present invention was to provide compositions which are distinguished by a combination of excellent mechanical performance, i.e. high notched impact strength, weld line strength, elongation at tear in the tensile test and stress cracking resistance under the action of chemicals, flame resistance down to thin wall thicknesses as well as good processability by the injection molding method, i.e. a large processing window.